The present invention relates to a parallel plate type oscillatory gyroscope, and more particularly, to a parallel plate type oscillatory gyroscope with a high detecting sensitivity.
Examples of conventional oscillatory gyroscopes includes a tuning-fork type gyroscope shown in FIG. 1 and a vibrating reed type gyroscope shown in FIG. 2.
As shown in FIG. 1, the tuning-fork type oscillatory gyroscope 21 includes a pair of driving piezoelectric ceramic plates 23, both base ends of which are connected to each other through a connection plate 22. The piezoelectric ceramic plates 23 are parallel to each other and their planes are normal to the X-axis, as shown in FIG. 1. A pair of detection piezoelectric ceramic plates are located on centers of the distal ends of the piezoelectric ceramic plates 23, respectively. The piezoelectric ceramic plates 24 are aligned in a plane normal to the Y-axis, which is perpendicular to the x-axis, as shown in FIG. 1. The piezoelectric ceramic plates 23 are applied with alternating voltage to vibrate in the positive and negative directions of the X-axis. If rotation about the Z-axis is imparted to the oscillatory gyroscope 21 the piezoelectric ceramic plates 24 distort and produce a voltage. Detection of this voltage permits a force acting on the piezoelectric ceramic plates 24, or, a Coriolis force Fc, to be sensed. The Coriolis force Fc is generally represented by the following formula (1): EQU Fc=2 mV.times..omega. (1)
where m indicates the mass of the oscillatory gyroscope 21; V the vibrational speed; and .omega. the angular velocity of the oscillatory gyroscope 21 about the Z-axis.
As shown in FIG. 2, a vibrating reed type oscillatory gyroscope 25 includes a vibrating reed type vibrator 26 in the form of a rectangular column, which is preferably made of a constant elasticity metal. Adhered to a pair of adjacent side faces of the vibrating reed type vibrator 26 are a pair of driving piezoelectric ceramic plates 27 (only one of them being shown in FIG. 2), respectively. Adhered to the remaining side faces are a pair of detection piezoelectric ceramic plates 28, respectively (only one of them being shown in FIG. 2). An alternating voltage is applied to the piezoelectric ceramic plates 27 to vibrate the vibrating reed type vibrator 26 in the positive and negative directions of the X-axis. When rotation about the Z-axis is imparted to the oscillatory gyroscope 26, the piezoelectric ceramic plates 28 distort and produce a voltage.
The piezoelectric ceramic plates 23, 24, 27 and 28 are formed from bulk PZT (lead zirconate titanate, or ceramics comprising a solid solution of lead titanate and lead zirconate). However, it is difficult to form bulk PZT into thin plates, so it is difficult to reduce the size of the oscillatory gyroscope.
Additionally, adhering the piezoelectric ceramic plates 27, 28 to the vibrator 26 increases the number of manufacturing steps, and generates dispersion in the detecting sensitivity due to adhesion accuracy, or, positional accuracy.
The Coriolis force Fc increases, as shown by the formula (1), in proportion to the mass m of the oscillatory gyroscope. As a result, as the mass m increases, the detection piezoelectric ceramic plates 24, 28 increase in amount of distortion, which improves the detecting sensitivity. To increase the mass of the oscillatory gyroscope, it is preferred to increase the amount of the base material for the bulk PZT. However, there is a limit in increasing the amount of the bulk PZT.
Further, the Coriolis force Fe increases in proportion to the vibrating speed V. As a result, the detecting sensitivity is improved. In order to increase the vibrating speed, it is preferred in the tuning-fork type oscillatory gyroscope to make the base material for the bulk PZT thinner. However, when made thinner, the piezoelectric ceramic plates 23 lose rigidity and become easy to distort. This distortion makes it difficult to obtain accurate vibrations on the piezoelectric ceramic plates 23 and is added to the distortion of the detection piezoelectric ceramic plates 24, which makes detection of voltage difficult.
An object of the present invention is to provide an oscillatory gyroscope having an improved detecting sensitivity.